1. Technical Field
The present invention relates to thin film transistors and, particularly, to a carbon nanotube based thin film transistor.
2. Discussion of Related Art
A typical thin film transistor (TFT) is made of a substrate, a gate electrode, an insulation layer, a drain electrode, a source electrode, and a semiconducting layer. The thin film transistor performs a switching operation. In use, the thin film transistor modulates carriers in an interface between the insulation layer and the semiconducting layer from an accumulation state to a depletion state, with voltage applied to the gate electrode. Thus, the thin film transistor can change the amount of the current between the drain electrode and the source electrode. In practical use, a high carrier mobility affect of the material of the semiconducting layer of the thin film transistor is desired.
Previously, the material of the semiconducting layer has been amorphous silicone (a-Si), poly-silicone (p-Si), or organic semiconducting material. The carrier mobility of an a-Si thin film transistor is relatively lower than a p-Si thin film transistor. However, the method for making the p-Si thin film transistor is complicated and has a high cost. The organic thin film transistor is flexible but has low carrier mobility.
Carbon nanotubes (CNTs) are a novel carbonaceous material and have received a great deal of interest since the early 1990s. Carbon nanotubes have interesting and potentially useful heat conducting, electrical conducting, and mechanical properties. Further, there are two kinds of carbon nanotubes: metallic carbon nanotubes and semiconducting carbon nanotubes determined by the arrangement of the carbon atoms therein. The carrier mobility of the semiconducting carbon nanotubes along a length direction thereof can reach about 1000 to 1500 cm2V−1s−1. Thus a thin film transistor adopting carbon nanotubes as a semiconducting layer has been produced.
A conventional carbon nanotube based thin film transistor is generally made by printing the mixture of carbon nanotubes and a polymer on a substrate to form a semiconducting layer. But the semiconducting layers of the conventional carbon nanotube based thin film transistor commonly include a plurality of metallic carbon nanotubes. This will result in current leakage from the source electrode to the drain electrode. Thus, the on/off current ratio of the thin film transistor using the carbon nanotube layer as a semiconducting layer is relatively low.
What is needed, therefore, is providing a carbon nanotubes based thin film transistor that has a better on/off current ratio.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present thin film transistor, in at least one form, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner.